Coronary artery disease is typically causes ischemia of the heart muscle by involving the coronary artery that is supplying the blood and nutrient to the heart muscle. The most typical etiological factor of such coronary artery diseases is arteriosclerosis. When plaque, formed by the mixing of cholesterol, other lipids, and a variety of components in the coronary artery and deposited on the inner lining of arterial walls, is excessively built up inside of the arterial lumen, the plaque undesirably causes an artery stenosis and ischemia of the heart muscle, thus making the heart muscle suffer lack of oxygen and nutritive substances. In the case of lack of oxygen and nutritive substance to the heart muscle due to ischemia of the heart muscle, a patient suffers angina pectoris or myocardial infarction, which may be fatal.
In the prior art, the non-surgical treatments of patients suffering from such coronary artery diseases use the two types of devices: an expandable balloon catheter or an expandable stent to enlarge the lumen and improve the angina, both being used for non-surgical insertion into a troubled coronary artery.
In the interventional treatment of a coronary artery disease using an expandable balloon, a guiding catheter is primarily inserted into the artery of the femoral region or the arm, and is secondarily positioned at the inlet of the coronary artery having the troubled lesion. In such a case, the term “lesion” means the focus or the narrowed or stenosed portion of the coronary artery due to built up plaque. After the guiding catheter positioning, a guide wire is navigated down into the coronary artery across the narrowed lesion site under the fluoroscopic guidance. Thereafter, a balloon-tipped catheter is inserted into the coronary artery over or along the guide wire until the catheter positioned at the lesion. The balloon is, thereafter, appropriately expanded to compress the plaque, and expands the narrowed or stenosed vessel to improve the perfusion in the heart muscle.
In case of the interventional treatment using a metallic stent, stent-mounted balloon catheter is inserted at the lesion of a troubled coronary artery after trials of balloon expansion and the balloon catheter with stent mounted is appropriately expanded and deployed at the lesion site. Therefore, the stent is permanently set in the lesion to expand the narrowed or stenosed vessel and allow a smooth circulation of blood in the coronary artery. The interventional treatment using such a stent is an effective treatment, as the stent maintains the expanded state of the vessel for a lengthy period of time. In comparison with the balloon catheter only, the treatment using such a stent reduces the possibility of recurrence of vessel narrowing. In addition, the stent buttresses the inner lining of the coronary arterial walls, and so the stent can be effective for treating a patient suffering from a complication after the procedure.
However, atherosclerotic arterial walls around the lesion are typically too rigid, so that they are apt to narrow or be constricted again due to an acute elastic recoil after an angioplasty Therefore, it is necessary for stents to sufficiently support the arterial wall in a radial direction and maintain the expanded state of the vessels for a desired lengthy period of time.
Another expected cause of the re-stenosis of the vessel after an angioplasty using an expandable stent is an excessive proliferation of a neo-intima within the stent. The stent is an in vivo foreign substance, and treatment with an insertion of a stent in the vessel inevitably causes morbid biological injury to the vessel. Therefore, intima is newly, inevitably produced within the vessel inside of the stent. Such a newly produced intima within the vessel is a so-called “neo-intima” in the description of this invention. Such a production of the neo-intima within the stent after an angioplasty using the stent is recognized as a normal healing response after injury. However, in the case of about 20˜30% of patients of the angioplasty using the stents, the neo-intima within a stent is excessively produced to cause the re-narrowing of the stented artery.
In an effort to effectively overcome such a re-stenosis of vessels due to an excessive production of the neo-intima within the stent, it has been required in the art to propose and use a stent designed for effective application of various anti-proliferative agents, which should reduce the excessive production of the neo-intima after the angioplasty.